This invention relates to a method and a system for biological treatment of water and wastewater, and particularly to a method and system for biological removal of nitrogen-containing impurities from low-temperature water and ground water.
Biological treatment of wastewater is well known. Also known are systems and methods for removal of nitrogen compounds, e.g. ammonia and other biodegradable matter from raw water supply for commercial, industrial and municipal users.
Certain raw water sources, for instance ground water sources in cold climate zones, provide raw water at a relatively low temperature, close to the freezing point (0° C. or 32° F.). At this temperature, some bacterial strains normally useful for biological degradation of water-borne impurities do not operate in an optimal manner. Nitrifying bacteria Nitrosomonas and Nitrobacter are normally not able to metabolize sufficiently at a temperature close to the water freezing point, at a temperature below approximately 5° C. On the other hand, at temperatures in the range about 5-40° C., these bacteria strains are active and degrade ammonia and other nitrogen impurities sufficiently well. The bacteria are aerobic and consume approximately 5 ppm of oxygen per 1 ppm of removed ammonia while also utilizing carbon source nutrients present in raw water.
While the relationship between bacterial efficiency, optimum temperature, oxygen and nutrient supply is known, the solutions vary depending on the source of raw water or wastewater and the scale of the systems. Specifically, there is a need for a low-cost system and method of biological treatment and purification of raw water derived from low-temperature sources such as ground water in cold climate areas, where the treatment efficiency depends in large part on the reliability of temperature control of the process.